Earth^47
WHAT ARE THE MOST VALUABLE MINERALS?
Some of the most valuable minerals are ores –
minerals that contain metals such as gold, iron, and
aluminium. Of these, gold is the most precious
because it is soft and easy to work and does not
tarnish. Other minerals are prized as. GEMSTONES.
Fossil fuels, such as coal, produce energy. Minerals
such as sulphur and mica are used in industry. Granite
and sandstone are used as building stones.About 50 of the 3,000 minerals found on
Earth are prized as gemstones. Although they
may not shine in their natural state, they can
be cut and polished to form sparkling stones.
Diamonds, the hardest minerals on Earth, are
made of pure, crystallized carbon and are
among the world’s most prized gemstones.Rocks are made of natural, non-living
chemical substances called minerals. Some
rocks contain only one mineral. For
example, marble is made of the white
mineral calcite. Most rocks, however,
contain. CRYSTALS of several
different minerals.HOW DO CRYSTALS FORM?
Crystals form as a molten solid (such as molten rock)
cools, or as liquid evaporates (turns into water vapour)
from a solution that contains a dissolved mineral. A
crystal grows as more and more atoms join onto the
basic lattice. Slow-growing crystals are larger than
those that form quickly.Crystals are solid, regular, geometric shapes
formed by most minerals. They have
smooth surfaces (called faces), straight
edges, and symmetrical corners because
they are built up from a regular framework
of atoms (tiny particles) called a lattice.WHERE ARE GEMSTONES FOUND?
Many gemstones are found in mountainous regions,
usually in rocks that have been subjected to great heat
or pressure. They are also found in the sediment on
lake and river beds. Diamonds are often mined from
rocks found deep underground.FIND OUT MORE. Atoms 157 • Chemistry 162 • Erosion 55 • Ice 58 • Volcanoes 44
4 THE GIANT’S CAUSEWAY
Made up of hexagonal (six-sided)
columns of the igneous rock
basalt, this famous rock
formation is found in
Northern Ireland.
AMETHYST CRYSTALS 3
These purple crystals are a type of quartz. They
formed in hot water, rich in the mineral silica.1 GOLD ORE
In most ores, metals are found mixed
with other substances. However, gold
occurs in a pure form in rocks such
as quartz (shown above).1 RUBY RED
Rubies are made of a mineral called corundum.
Rare, deep-red rubies are precious stones, as are
diamonds and emeralds.GEMSTONES
CRYSTALS
MINERALS
Pyramid-
shaped
amethyst
crystalsGoldQuartzrocks